1. Field of the Invention
The present invention generally concerns the forming of concrete slabs with a light-gage-steel form-set that defines a given geometry upon assembly.
The present invention particularly concerns a form set made up, as much as possible, from girt members that are normally, and will normally be, used in the construction of the building atop a concrete slab foundation.
The present invention further particularly concerns hardware that interconnects foundation form members while also fixing the locations of foundation anchor bolt elements in a manner exactly corresponding to connections of the structural frames of the building.
2. Description of the Prior Art
While much prior art can be found in the field of slab foundations and related concrete work, the commercial success of contemporary proprietary systems which form a concrete-slab-on grade is limited. The primary reasons for this are that the proprietary systems tend to be expensive, contrived, and inflexible. Furthermore, forming a concrete slab on a prepared building pad is not a significant engineering feat, and so is generally endeavored with simple boards and stakes.
The board and stake concept offers design flexibility, but it does have significant drawbacks. These drawbacks include: wasted labor to define and check geometry, poor accuracy of surfaces and embedded hardware, difficulty in adjusting form locations after stakes are set, and inconsistent repeatability for multiple units. Back injury, caused by pulling a conventional stake out of the ground, is a common complaint in the foundation business. Poor foundation accuracy is always a concern, and it has a more consequential negative affect on the framing process for a structure of light gage metal members. This is because the framing assemblages of these members tolerate little dimensional error at the points of support.
Established proprietary concrete forming systems include such ones as xe2x80x98Metaformxe2x80x99, which are of folded sheet metal. Lengths are generally in 10xe2x80x2 increments, which is the length of the brake that folds the sheet metal. For a long run of perimeter form this results in frequent potential segmental kinks. Conforming to custom dimension and design requires the cutting up of relatively expensive lengths of form. Stakes must be placed only at specific holder locations provided on the forms, and no subsequent relative horizontal adjustment is possible. If a rock or obstruction happens to be at one of these specific locations, then one must compromise either form location or stake support.
Solutions addressing the need to adjust forms relative to stakes include the system disclosed in Canadian patent 1,145,179 by Breitenbach, issued Apr. 26, 1983. This apparatus allows adjustment of form location subsequent to setting of stakes, by a system of supporting yokes consisting of bars, sleeves, and brackets. This type of a solution involves one or a pair of sets of moving parts for each direction of adjustment. Each supporting assemblage is subject to unwanted lateral movement due to the fact that the each of the supporting stake pairs are required to be essentially parallel for vertical adjustment of the yoke, which attaches to them above the forms. Stakes in loose soils simply do not hold up to this kind of side cantilever loading. Even bending of the stakes can be enough of a problem, given the relatively high point of attachment. Each of these assemblages is heavy, clumsy, relatively expensive, and an obstruction to the concrete work, especially for slab-on-grade foundations. There are too many parts to buy, clean, and maintain.
A somewhat simpler proprietary forming method offers subsequent adjustment in the vertical direction only. This is disclosed in U.S. Pat. No. 3,397,494, Waring, issued Aug. 20, 1968. With this system, vertical support to a proprietary perimeter member is provided with rods having machine thread. These rods thread into bearing pads that sit upon the earth, and then support the special cast in place perimeter member directly. No allowance is provided for rod location. It must be directly at a hole in the member, regardless of what local anomaly or rock may be at the ground below that point. The rod supports offer little resistance to uplift from the buoyant forces of concrete placement, because they do not have threads capable of threading into earth, and so are not used in that manner. This support offers essentially no lateral force resistance. In fact, the system requires a redundant conventional perimeter form board with conventional stakes, et cetera, for structural stability. The main purpose of the present invention is to provide placement of a cast in-situ foundation perimeter for a proprietary wall system which requires a special recessed ledge.
For slab-on-grade foundations, most contractors prefer to continue to form with simple boards and stakes, in spite of the drawbacks, because they do not impose a lot of contrivance, have a low initial cost, and provide flexibility in geometry. Those in the trades have grown to accept the challenges of building foundations with a most primitive technology. It is generally understood that foundation construction includes performing redundant efforts at determining geometry, having a difficult time making geometrical adjustments, and then getting complaints about accuracy from the people building the structure atop anyway. In truth, all of these problems really can be solved without forcing a lot of limitations and contraptions upon the foundation builder, as the following discussion will illustrate.
In order to evaluate a new foundation construction practice, it is sensible to first examine some contemporary needs of the industry.
Tract home builders most often build slab-on-grade foundations. Normally, a building pad is created for each unit. This pad is typically graded so as to completely facilitate slab-on-grade foundation construction. Identical unit footprints, and mirrored versions, are repeated often. The foundation forming method should effectively address this circumstance.
Homes built today tend to have more seismic hardware anchored in the foundation than earlier homes did. Increasingly, post-tension slab-on-grade foundations are being built in order to achieve economy at sites having expansive soil conditions. All of the post-tension anchors must be located correctly along the perimeter form, and in conjunction with the conventional hardware embedments. In general, more connections located in a tighter space demands more accuracy of the foundation forming method which locates these items. Additionally, the task of physically locating an element of hardware is performed very often. So, the task must be made to be as easy and repeatable as possible.
A growing number homes are being framed with members of cold-formed light-gage steel. The framing of these homes requires greater accuracy than most foundation contractors will deliver, particularly for the cost effective xe2x80x98panelizedxe2x80x99 structures (the metal stud walls are framed in a shop and erected at site). For the increasingly common xe2x80x98panelizedxe2x80x99 structure, a very accurate foundation, to the last hardware embedment, is required for cost effective construction. For repeat units of xe2x80x98panelizedxe2x80x99 homes, the accuracy must be such that entire buildings and foundations be considered as interchangeable parts, if true production building is to occur.
An important component of foundation accuracy is easy adjustment of location of foundation forms, so that needed adjustments are made rather than ignored. For custom built structures, provision for easy adjustment of foundation forms is significant. This is because, compared to repetitive construction, relatively far more labor tends to be expended on the custom geometry definition. So, the ability to have adjustment after forms are initially set up, provides a big labor savings for even one unit. It is best if all the foundation form support locations can be adjusted simultaneously. This way an entire lightweight forming unit, which is internally collocating, can be assembled whole, floating on supports, before being committed to the exact permanent placement.
Most contemporary post-tension slab-on-grade foundation construction is built on a flat-graded earth pad without trenches. This increasingly popular method requires no lay out of trenches, so a foundation forming method which does not require the lay out of any geometry at all, can provide significant labor-saving benefit to the foundation construction process.
The present invention provides the fastest means possible of constructing a concrete slab foundation. The process is more convenient and less injurious than conventional methods. The investment is less and the utility more diverse than with other proprietary methods. The results are more reliable and accurate. Components of the present invention offer novel utility independently, and with elements of co-pending patent applications, they offer substantial benefit for other types of foundations.
The present invention utilizes the increasingly available light-gage roll-formed steel members as concrete forms. They are low cost, light-weight, and are supplied in any desired lengths. These standardized xe2x80x9cCxe2x80x9d shaped sections are supported by exceptionally simple components which allow subsequent adjustment of forms relative to stakes, in all three orthogonal directions.
Other elements of the present invention combine with the form members to create a collocating-upon-assembly forming unit for an entire slab foundation. This forming unit may be assembled while floating on supports, and then adjusted into place. It can be built to be light-weight enough to allow a crew to carry it whole from unit to unit, as if it were a large cookie cutter.
With the present invention, adjustments to form locations are facilitated by the use of coarsely threaded rods which offer support directly. This is because the same adjustment rods which connect to form components, also thread directly into the earth. Threading into earth improves resistance to buoyant forces from concrete placement, and thus facilitates use of light-weight forms. The threaded stakes may also be angled outward so as to buttress the forms directly. They are much easier to get into and back out of the ground than conventional stakes are. Threaded stakes offer significant improvements to the construction of most any type of in-situ concrete foundation.
The present invention requires less labor than any other method to build a concrete slab foundation. It will please any builder with the inherent, repeatable accuracy. Elements of the present invention provide labor-saving and quality-enhancing utility for slab foundation.
It may still further be recognized that contemporary manufacturers of xe2x80x9cpre-engineeredxe2x80x9d steel moment-frame commercial buildings go through sophisticated processes of creating a kit of parts efficiently made to particular building dimensions. It seems a waste of effort for foundation contractors to go through the entire process again, far less efficiently and much less accurately, when the same manufactured parts are shipping to the project site anyway, and might potentially serve proficiently as the forms for construction of the building""s foundation forms.
It would therefore be desirable if some hardwarexe2x80x94xe2x80x9cfoundation form-set fixturesxe2x80x9dxe2x80x94would permit use of these pre-manufactured building elements in the production of a slab foundation. The use of such hardware elements in assembling the building elements would preferably be simple, and foolproof.
It would be a further great boon if, as well serving to permit use of existing modular building elements in forming a dimensionally accurate concrete slab foundation, the foundation form-set which fixtures would serve to place the all important building anchor bolts exactly in place, thereby facilitating later erection of the building.
If a clearly superior slab foundation so produced could also be constructed with (i) less labor and/or (ii) less skill, then this would also be an advantage.
The present invention contemplates a system and method for forming concrete slab foundations for commercial buildings having a steel moment-frame structure. In accordance with the invention, cold-formed-steel framing members, such as the wall girts shipped with a particular building package, are first used as slab foundation forming elements before these members are later framed into a building. By use of special hardware fixtures, the system and method of the invention serve to both (i) define foundation geometry upon a simple assembly of the forming elements of regular geometry, and (ii) place necessary anchoring hardware in locations precisely corresponding to the structural frame of the building.
1. A System and Method for Forming Foundation Slabs from Metal Girts Otherwise Useable as Structural Elements in a Building
In its principal aspect, the present invention is embodied in a system, and in a method, for forming foundation slabs from metal girts otherwise useable, and used, as structural elements in a building.
The preferred system includes a number of metal girts, otherwise usable as structural elements in a building, that are temporarily laid out in the pattern of a perimeter foundation to the building. A number of connectors serve to connect the multiplicity of girts one to the next, each at an identical separation as the girts would otherwise have in a building erected with the girts.
The collective connected girts constitute a frame of dimensions exactly as correspond to a given finished building erectable with the girts. This frame of connected girts is then supported level above the surface of the earth, where it then becomes and constitutes a form suitable to define the perimeter of a foundation slab.
Flowable hardenable construction material is subsequently placed upon the surface of the earth within the supported form, and hardens as a slab. The selfsame girts as were both (i) joined, and (ii) supported as the form for the slab, are disconnected from each other and removed from the sides of the hardened slab. The girts may then be used as structural components of a building that is erected upon the very slab that the girts helped to form.
In particular, the preferred metal girts are elongate steel members with bolt holes of a predetermined pattern and spacing at each end. With girts of this type the connectors are made from (i) steel plates having bolt holes, and (ii) bolts. The bolt holes in the steel plates are in a pattern, and at an offset relative to the ends of the plates, as serve to connect the multiplicity of girts one to the next at an identical separation as the girts would otherwise (or will) have in a building erected with the girts. This simple concept is important: the girts are not merely connected but are connected at the same relative spacing as they will be in the building.
Further in particular, the support of the frame of connected girts level above the surface of the earth (as the form) is preferably realized by, in part, a number of (preferably threaded) stakes that are driven (or, preferably, screwed) within the earth. Meanwhile, each of a number of connection elementsxe2x80x94preferably in the form of bent metal plates with tabs when used with girts having xe2x80x9cCxe2x80x9d-channel lipsxe2x80x94serve to engage and to hold an associated one of the many girts. A number of xe2x80x9cstopsxe2x80x9d slip and thread the stakes, serving ultimately hold each of the connection elements and the girt which the connection element engages and holds at a selected height above the earth. By this manner of support the collectively held frame of girts is elevated above the surface of the earth, and becomes a form.
Still further in particular, the girt connectors are preferably made as (i) an xe2x80x9cLxe2x80x9d-shaped first plate memberxe2x80x94called a xe2x80x9cform connector/anchor bolt locatorxe2x80x9dxe2x80x94for connecting one girt to the next at their butt ends by action of bolt holes that are located to accept bolts that hold the abutting girts at a same separation as the girts will later assume within the later-erected steel building, plus (ii) a second plate memberxe2x80x94called a xe2x80x9cclamp platexe2x80x9dxe2x80x94for sandwiching end regions of connected girts between itself and the first plate member, and (iii) bolts for bolting the first plate member to the second plate member.
The second plate member may optionally have a vertical channel (called a xe2x80x9cstake channelxe2x80x9d), in which case the connectors may further include yet another, third, plate memberxe2x80x94called a xe2x80x9cstake platexe2x80x9dxe2x80x94in the substantial contour of one-half of a common hinge. This third plate member connects to an upright girt at its end region by action of bolt holes and bolts while presenting outboard of this region a vertical bore. A rodxe2x80x94or a xe2x80x9cconventional stakexe2x80x9d as opposed to the somewhat different stakes that preferably support the formxe2x80x94passes through the bore of this third plate member and downward into a cavity formed between the first plate member and the vertical channel of the second plate member. The rod thus serves to connect (i) the upright girt to (ii) two abutting girts at and from a position above the abutting girts. In this superior position the upright gird serves as a screed, and is so called.
The preferred method of the present invention for making a foundation slab upon the surface of the earth preferably includes the following steps. A number of metal girts that are otherwise usable as structural elements in the erection of a building are laid out in the pattern of a perimeter to a slab foundation to a building. These girts are connected, one to the next and at an identical separation as the girts would otherwise have in the building erected with the girts, by a similar number of connectors. The collective connected girts constitute a xe2x80x9cframexe2x80x9d. This frame has dimensions exactly as correspond to a given finished building erectable with the girts.
The frame of connected girts is then supported level above the surface of the earth. When so supported the frame becomes and constitutes a xe2x80x9cformxe2x80x9d, which form defines the perimeter of a foundation slab.
Flowable hardenable construction material is then placed upon the surface of the earth within the supported form. This material subsequently hardens, producing a slab.
Finally, the selfsame girts as were both (i) joined, and (ii) supported, to make the form for the slab, are disconnected and removed, permitting that they should next be used as structural components in the erection of a building upon the slab.
2. A Monolithic Slab Foundation Perimeter Form
In another of its aspects, the present invention may be considered to be embodied in a monolithic slab foundation perimeter form.
The preferred from includes a large number of girts, being elongate metal members used in the erection of a steel building. These girts are laid end to end in the pattern of a perimeter foundation.
An xe2x80x9cLxe2x80x9d-shaped connector member serves to join one girt to the next at their butt ends, This member has in a first leg of its xe2x80x9cLxe2x80x9d shape bolt holes that are precisely located to accept bolts holding the abutting girts at a same separation as they will later assume within a later-erected steel building. It preferably also has in a second, orthogonal, leg of its xe2x80x9cLxe2x80x9d shapexe2x80x94which leg is positionally disposed towards a foundation to be pouredxe2x80x94a hole for the inspection of the placement of flowable foundation material.
This xe2x80x9cLxe2x80x9d-shaped connector member""s first leg bolt holes are preferably threaded, permitting that bolts may readily be threaded within these holes so as to attach the girts to the connector member, and to each other, for temporary use as a foundation form. Moreover, the bolts may subsequently be readily backed out both from a hardened formed foundation and from the connector member, releasing the attached girts and permitting re-use of both girts and bolts.
The xe2x80x9cLxe2x80x9d-shaped connector member""s second leg preferably further has, in addition to the inspection hole, at least one hole, and more preferably a number of holes, each for receipt of a foundation anchor bolt.
These and other aspects and attributes of the present invention will become increasingly clear upon reference to the following drawings and accompanying specification.